This invention relates generally to turbine engines and, more particularly, to methods and apparatus for fabricating a nozzle singlet for use with turbine engines.
At least some known turbine engines include turbine nozzle assemblies having a plurality of nozzle singlets that extend circumferentially around the turbine. The nozzle singlets are positioned throughout various stages of the turbine to facilitate channeling air downstream towards turbine blades. Specifically, adjacent nozzle singlets are circumferentially spaced and oriented to define a throat through which hot gases are channeled. An area of the throat may vary between different known engines or within different areas of an engine as the area of the throat is a factor that contributes to determining a mass flow of hot gas exiting the throat. The throat area is proportional to the throat width. As such the throat width can be adjusted to control a ratio of mass flow entering the throat to mass flow exiting the throat.
Known nozzle singlets are typically fabricated from two machined singlets. These singlets are cast from a unitary piece to include an inner band, an outer band, and at least one airfoil extending therebetween. Cooling holes are then machined into the nozzle singlet to facilitate cooling during engine operations. Generally, the cooling holes are machined in a pattern that is identical for each nozzle singlet machined. Following assembly of the nozzle singlets to create the nozzle singlet, the inner and outer bands of the nozzle singlet are then reshaped through grinding and/or machining to position the airfoil to provide a desired throat width when the engine is assembled. Specifically, the inner and outer bands are fabricated to be positioned substantially flush with a circumferentially-adjacent nozzle singlet to provide the desired airfoil angle. Because the throat width, and subsequently, the airfoil angle, may differ from engine to engine, the inner and outer bands may be machined at different angles. However, machining the bands to accommodate at least some desired airfoil angles may result in a need to adjust the cooling hole pattern to avoid having the cooling holes obliterated during machining.